1. Field of the Invention
This invention relates to a power controlling unit that can control a power supplied to a heater or the like, a power controlling method by using the power controlling unit, and a thermal processing unit incorporating the power controlling unit.
2. Disclosure of the Prior Art
As a manufacturing unit for semiconductor devices, there is known a vertical thermal processing unit that can conduct a thermal process in a batch manner.
Fig.9 schematically shows such a conventional vertical thermal processing unit and a power controlling unit used with the conventional vertical thermal processing unit. The conventional thermal processing unit comprises a tubular reaction tube 11, which is made of for example crystal. A wafer boat (not shown) supporting many semiconductor wafers is loaded into the reaction tube 11 through an under portion of the reacting tube 11. A heater 12 consisting of three zone-heaters 12a, 12b and 12c surrounds a lateral (peripheral) surface of the reaction tube 11. The reaction tube 11 and the heater 12 form a heating furnace 13. Heat values generated by the respective zone-heaters 12a, 12b and 12c are adjusted by the power controlling unit that is connected to the respective zone-heaters 12a, 12b and 12c. 
Thus, a suitable thermal process can be conducted to the wafers loaded into the reaction tube 11.
The power controlling unit comprises a power transformer 15 of a fixed voltage and a power supply source 14 arranged at a primary side of the power transformer 15. Power is adapted to be delivered from the power supply source 14 to the respective zone-heaters 12a, 12b and 12c via the power transformer 15. That is, volume of the power supplied to the respective zone-heaters is controlled by controlling timings to turn on or off respective semiconductor switches in a switch unit 16 arranged at a secondary side of the power transformer 15. In addition, protective units from overcurrent (for example fuses) 17a, 17b and 17c are disposed between the power transformer 15 and the switch unit 16.
There are known a method of employing a phase control SCR (silicon controlled rectifier) for the semiconductor switches in the switching unit 16 and a method of employing a zero-cross control SCR for the semiconductor switches in the switching unit 16. For example, the former method may be used in a case wherein the heating furnace 13 is formed into a rapid-heating furnace having a great rising rate of temperature, for example about 100xc2x0 C./minute. The latter method may be used in a case wherein the heating furnace 13 is a general furnace.
In the phase control SCR, the switch for the power supply can be turned ON or OFF at any timing in one cycle of 360 degrees. Thus, higher resolution can be achieved. On the other hand, in the zero-cross control SCR, the switch for the power supply can be turned ON or OFF only at a timing when the voltage is zero bolt in one cycle. For example, if a frequency of the power supply source is 50 Hz, volume of the supplied power can be changed only according to 50 ranks per 1 second, by turning ON or OFF the switch every cycle of the power supply source. For example, if the switch is turned ON at the first cycle, turned OFF at the second cycle, and remains OFF at the other cycles, the volume of the supplied power is 2% of a maximum volume thereof (100%xc3x971/50). If the number of cycles when the switch is turned ON or remains ON is increased, the volume of the supplied power is also increased by 2% (2, 4, 6, . . . , 100%).
In general, a heater used in the rapid-heating furnace has a great changing rate of resistance against temperature. Thus, in order to control temperature of the heater stably, it is preferable that the phase control SCR that can achieve higher resolution is used. However, there is a problem that phase control SCR may output higher harmonic waves of not negligible levels. Thus, in a conventional unit using the phase control SCR, large-scale active filters are used to remove the higher harmonic waves. Such a unit for removing the higher harmonic waves is expensive, that is, there is also a problem about cost.
On the other hand, if the zero-cross control SCR is used, levels of generated higher harmonic waves are less than those in the case wherein the phase control SCR is used. However, because the switch for the power supply may be turned ON or OFF only one time per 1 cycle in order to adjust the volume of the supplied power, resolution of the supplied power depends on the frequency (cycle) of the power supply source. That is, it is difficult to control the supplied power finely. Thus, it is difficult to use the zero-cross control SCR for the rapid-heating furnace.
This invention is intended to solve the above problems effectively. An object of this invention is to provide a power controlling unit and a method thereof that can prevent higher harmonic waves from being generated and that can achieve higher resolution. Another object of this invention is to provide a thermal processing unit that can control temperature thereof stably by using the above power controlling unit.
This invention is a power controlling unit comprising: a power transformer having a primary side that can be connected to an Alternating-current power supply source, and a secondary side having an end side provided with a terminal that can be connected to an end of an object whose power is to be controlled, and the other end side provided with a plurality of voltage taps; a switching part disposed between the plurality of voltage taps and the other end of the object, the switching part selecting one from the plurality of voltage taps in order to connect the one to the other end of the object; a storing part that stores a plurality of output values for the object and a plurality of switching patterns which correspond to the plurality of output values respectively, each of the plurality of output values being set correspondingly to a unit of control consisting of a plurality of cycles of a frequency of the Alternating-Current power supply source, each of the plurality of switching patterns defining a voltage tap that should be selected if any in each of the plurality of cycles in order to achieve the corresponding output value; and a switching controlling part that can read a switching pattern corresponding to an output value from the storing part and that can control the switching part based on the switching pattern.
Alternatively, this invention is a power controlling unit comprising: a power transformer having a secondary side that can be connected to an object whose power is to be controlled, and a primary side having an end side provided with a terminal that can be connected to an end of an Alternating-Current power supply source, and the other end side provided with a plurality of voltage taps; switching part disposed between the plurality of voltage taps and the other end of the Alternating-Current power supply source, the switching part selecting one from the plurality of voltage taps in order to connect the one to the other end of the Alternating-Current power supply source; a storing part that stores a plurality of output values for the object and a plurality of switching patterns which correspond to the plurality of output values respectively, each of the plurality of output values being set correspondingly to a unit of control consisting of a plurality of cycles of a frequency of the Alternating-Current power supply source, each of the plurality of switching patterns defining a voltage tap that should be selected if any in each of the plurality of cycles in order to achieve the corresponding output value; and a switching controlling part that can read a switching pattern corresponding to an output value from the storing part and that can control the switching part based on the switching pattern.
According to the above inventions, higher resolution can be achieved so that supplied power can be controlled more finely. For example, if the object whose power is to be controlled is a heater consisting of a resistance heating element, temperature of the heater can be controlled stably, even if the heater has a great changing rate of resistance against temperature.
Preferably, respective load powers that are generated when the respective voltage taps of the power transformer are selected in turn are set to reduce by half from a maximum thereof to a minimum thereof in turn. In the case, binary numbers of logic circuit can be used for processes effectively.
The respective voltage taps of the power transformer may be set correspondingly to a desired controlling manner for the object whose power is to be controlled. For example, respective load currents that are generated when the respective voltage taps of the power transformer are selected in turn are set to reduce by half from a maximum thereof to a minimum thereof in turn. Alternatively, respective load voltages that are generated when the respective voltage taps of the power transformer are selected in turn are set to reduce by half from a maximum thereof to a minimum thereof in turn.
In addition, preferably, the switching controlling part can control the switching part to switch the voltage taps when a voltage waveform at the secondary side of the power transformer crosses zero volt. Furthermore, preferably, the order of the voltage taps that are connected (turned ON) is set in such a manner that voltage difference between two voltage taps of any adjacent two cycles is as small as possible. In the case, higher harmonic waves, which may be generated because of a great voltage difference, can be more effectively prevented from being generated.
In addition, this invention is a method of controlling a power supplied to an object whose power is to be controlled, by using a power controlling unit including: a power transformer having a primary side that can be connected to an Alternating-Current power supply source and a secondary side having an end side provided with a terminal that can be connected to an end of the object, and the other end side provided with a plurality of voltage taps; a switching part disposed between the plurality of voltage taps and the other end of the object, the switching part selecting one from the plurality of voltage taps in order to connect the one to the other end of the object; a storing part that stores a plurality of output values for the object and a plurality of switching patterns which correspond to the plurality of output values respectively, each of the plurality of output values being set correspondingly to a unit of control consisting of a plurality of cycles of a frequency of the Alternating-Current power supply source, each of the plurality of switching patterns defining a voltage tap that should be selected if any in each of the plurality of cycles in order to achieve the corresponding output value; and a switching controlling part that can read a switching pattern corresponding to an output value from the storing part and that can control the switching part based on the switching pattern; the method comprising: a setting step of generating an output value to the object correspondingly to the unit of control consisting of the plurality of cycles of the frequency of the Alternating-Current power supply source; a reading step of reading a corresponding switching pattern from the storing part based on the generated output value; and a switching step of changing the voltage taps to be connected to the other end of the object, based on the read switching pattern.
Preferably, the switching step is conducted when a voltage waveform at the secondary side of the power transformer crosses zero volt.
Alternatively, this invention is a method of controlling a power supplied to an object whose power is to be controlled, by using a power controlling unit including: a power transformer having a secondary side that can be connected to the object, and a primary side having an end side provided with a terminal that can be connected to an end of an Alternating-Current power supply source, and the other end side provided with a plurality of voltage taps; a switching part disposed between the plurality of voltage taps and the other end of the Alternating-Current power supply source, the switching part selecting one from the plurality of voltage taps in order to connect the one to the other end of the Alternating-Current power supply source; a storing part that stores a plurality of output values for the object and a plurality of switching patterns which correspond to the plurality of output values respectively, each of the plurality of output values being set correspondingly to a unit of control consisting of a plurality of cycles of a frequency of the Alternating-Current power supply source, each of the plurality of switching patterns defining a voltage tap that should be selected if any in each of the plurality of cycles in order to achieve the corresponding output value; and a switching controlling part that can read a switching pattern corresponding to an output value from the storing part and that can control the switching part based on the switching pattern; the method comprising: a setting step of generating an output value to the object correspondingly to the unit of control consisting of the plurality of cycles of the frequency of the Alternating-Current power supply source; a reading step of reading a corresponding switching pattern from the storing part based on the generated output value; and a switching step of changing the voltage taps to be connected to the other end of the object, based on the read switching pattern.
In the case too, preferably, the switching step is conducted when a voltage waveform at the secondary side of the power transformer crosses zero volt.
Alternatively, this invention is a thermal processing unit comprising; a reacting container that can conduct a thermal process to an object to be processed; a heater arranged surrounding the reacting container; a power transformer having a primary side that can be connected to an Alternating-Current power supply source, and a secondary side having an end side provided with a terminal connected to an end of the heater, and the other end side provided with a plurality of voltage taps; a switching part disposed between the plurality of voltage taps and the other end of the heater, the switching part selecting one from the plurality of voltage taps in order to connect the one to the other end of the heater; a storing part that stores a plurality of output values for the heater and a plurality of switching patterns which correspond to the plurality of output values respectively, each of the plurality of output values being set correspondingly to a unit of control consisting of a plurality of cycles of a frequency of the Alternating-Current power supply source, each of the plurality of switching patterns defining a voltage tap that should be selected if any in each of the plurality of cycles in order to achieve the corresponding output value; and a switching controlling part that can read a switching pattern corresponding to an output value from the storing part and that can control the switching part based on the switching pattern.
Alternatively, this invention is a thermal processing unit comprising; a reacting container that can conduct a thermal process to an object to be processed; a heater arranged surrounding the reacting container; a power transformer having a secondary side connected to the heater, and a primary side having an end side provided with a terminal that can be connected to an end of an Alternating-Current power supply source, and the other end side provided with a plurality of voltage taps; a switching part disposed between the plurality of voltage taps and the other end of the Alternating-Current power supply source, the switching part selecting one from the plurality of voltage taps in order to connect the one to the other end of the Alternating-Current power supply source; a storing part that stores a plurality of output values for the heater and a plurality of switching patterns which correspond to the plurality of output values respectively, each of the plurality of output values being set correspondingly to a unit of control consisting of a plurality of cycles of a frequency of the Alternating-Current power supply source, each of the plurality of switching patterns defining a voltage tap that should be selected if any in each of the plurality of cycles in order to achieve the corresponding output value; and a switching controlling part that can read a switching pattern corresponding to an output value from the storing part and that can control the switching part based on the switching pattern.
In these cases, preferably, respective load powers that are generated when the respective voltage taps of the power transformer are selected in turn are set to reduce by half from a maximum thereof to a minimum thereof in turn. Alternatively, respective load currents that are generated when the respective voltage taps of the power transformer are selected in turn are set to reduce by half from a maximum thereof to a minimum thereof in turn. Alternatively, respective load voltages that are generated when the respective voltage taps of the power transformer are selected in turn are set to reduce by half from a maximum thereof to a minimum thereof in turn.
In addition, preferably, the switching controlling part can control the switching part to switch the voltage taps when a voltage waveform at the secondary side of the power transformer crosses zero volt.